The improved fastener element and panel assembly and method of this invention may be utilized to install a fastener in a relatively thick panel or metal plate to provide a rigid assembly having excellent pull-out and push-through strength and torque resistance and which avoids deformation, damage or even marring of the panel, as may be required for applications where the panel or plate includes a bearing surface, for example, such as a wheel hub assembly.
The assignee of the present application and its related companies have developed numerous self-piercing and clinching fastener systems for various applications, including self-piercing male and female fastener systems which are generally adapted for attachment of the fastener to relatively thin panels such as used in mass production applications by the automotive and appliance industries. The integrity of the joint established between the fastener and panel generally depends upon deformation of the metal panel. In the PIERCEFORM(copyright) fastener systems of the assignee and its related companies, for example, the fastener includes a body portion, an integral radial flange portion and a tubular barrel portion integral with the flange portion, which pierces the panel and is deformed radially outwardly in an annular female die member into an outwardly opening hook-shape which captures and deforms the panel surrounding the pierced panel opening to form a rigid fastener and panel assembly having excellent pull-out and push-through strength. Examples of such fastener systems may be found in U.S. Pat. Nos. 4,831,698 and 4,915,558. As used herein, xe2x80x9cpush-through strengthxe2x80x9d refers to the force required to push the fastener through the panel assembly in the direction the fastener is installed in the panel and xe2x80x9cpull-out strengthxe2x80x9d refers to the force required to pull the fastener out of the assembly in a direction opposite to the direction the fastener is installed in the panel. Torque resistance may also be provided in such fastener systems by ribs or splines generally located on the flange portion adjacent the tubular barrel portion. These fastener systems include self-piercing male fasteners, such as studs and bolts, and female fasteners including threaded and unthreaded nuts. The assignee of this application also developed self-piercing and self-clinching nut fasteners having a pilot portion and an integral flange portion, wherein the pilot portion is installed in a press which may also be utilized to form the metal panel during installation of the fastener as disclosed in U.S. Pat. No. 4,971,499. The pilot portion pierces the panel and the panel adjacent the pierced panel opening is substantially simultaneously deformed into grooves located either in the flange portion adjacent the pilot portion or in the pilot portion by a die member generally referred to as a die button. However, such self-attaching fasteners were also adapted for relatively thin metal panels as required for such applications.
Self-clinching fastener systems have also been developed by the assignee and its related companies which may be utilized in thicker metal panels, but which also generally rely upon some deformation of the panel which limits the range of panel thicknesses to which the fastener may be attached. These fastener systems developed by the assignee and its related companies, particularly Multifastener Corporation, the predecessor in interest of the assignee, and Profil Verbindungstechnik GmbH and Co. KG have been commercially successful, particularly in mass production applications of the type described above. However, there has been a long felt need for a fastener system, wherein the fastener may be installed in a relatively thick panel or plate and which avoids deformation of the panel.
The fastener of the fastener and panel assembly and method of this invention may be formed by conventional die forming techniques and preferably includes a body portion and an integral tubular barrel portion, preferably coaxially aligned with the body portion. In the disclosed embodiment, the exterior surface of the body portion is generally cylindrical and the exterior surface of the tubular barrel portion is also cylindrical and continuous with the external surface of the body portion. In the most preferred embodiment, the exterior surface of the body portion includes a conical surface having a major diameter adjacent the tubular barrel portion as described further below. However, the body portion may also be polygonal having six or eight sides, for example, and it is believed that the tubular portion could also be polygonal depending upon the application, although it is believed that a tubular barrel portion having a cylindrical exterior surface will be preferred in most applications even where the body portion is polygonal. The disclosed embodiment of the fastener element is a male fastener having a shank portion integral with the body portion opposite the tubular barrel portion which may be threaded, as disclosed. The shank portion preferably has an exterior diameter less than the exterior diameter of the body portion to permit installation of the fastener element in a panel without deforming the panel as disclosed. However, the method of installing a fastener element and fastener and panel assembly of this invention may also be used with a female fastener element, wherein the body portion includes a bore therethrough which may either be prethreaded or threaded following installation by conventional thread forming or thread rolling techniques which would avoid concern regarding distortion of the threads of a prethreaded bore particularly in the most preferred method of this invention, wherein the body portion is deformed radially outwardly to provide a secure interference fit with the opening through the panel.
The method of attaching a fastener element to a panel of this invention includes inserting the free end portion of the tubular barrel portion of the fastener element through an opening in the panel into a die member located opposite the panel opening. The method then includes substantially continuously permanently deforming the tubular barrel portion adjacent the free end portion radially inwardly and toward the body portion and the midportion of the barrel portion radially outwardly in the die member to deform the barrel portion until the midportion has a diameter greater than the panel opening and the free end portion is deformed radially inwardly to limit radial inward flexure of the midportion which would permit withdrawal of the fastener element from the panel opening. In the preferred method of this invention, the body portion located in the panel opening is supported by a second die member opposite the tubular barrel portion and the die members are driven relatively toward one another to simultaneously deform the tubular barrel portion in the first die member as described above and the body portion adjacent the second die member is deformed radially outwardly to form a secure interference fit between the fastener element and the panel opening which provides excellent push-through strength and torque resistance.
In this embodiment, the exterior surface of the body portion includes a conical surface having a major diameter adjacent the tubular barrel portion generally equal to or even slightly larger than the cylindrical diameter of the bore or opening through the panel, thereby forming a secure interference fit or mechanical interlock between the exterior surface of the fastener element and the full length of the body portion which provides excellent push-through strength and torque resistance. Where the fastener element is a male fastener element having an integral shank portion extending from the body portion opposite the tubular barrel portion, the die member preferably has an annular die surface surrounding the shank portion which engages the body portion and which avoids contact with the adjacent surface of the panel. In this embodiment, the first die member which receives the free end portion of the tubular barrel portion is driven toward the second die member which supports the body portion to deform the tubular barrel portion as described without contacting the adjacent surface of the panel. The method of this invention thus avoids any contact with the panel or deformation of the panel, but provides a secure fastener element and panel assembly having excellent push-out and pull-through strength and torque resistance with relatively thick panels or plates.
In the preferred method of attaching a fastener element to a panel of this invention, the method includes forming a chamfer, preferably a conical chamfer in the panel opening adjacent the tubular barrel portion and deforming the midportion of the tubular barrel portion radially outwardly into the chamfer to overlie the panel spaced from the chamfer to provide excellent pull-through strength. Alternatively, the midportion of the tubular barrel portion may be deformed radially outwardly to overlie the panel adjacent the panel opening; however, a conical chamfer supports the radially outwardly bowed portion of the tubular barrel portion and avoids stress fracture of the tubular barrel portion which may be generated by a relatively sharp edge under extreme conditions.
In certain applications, it is desirable to prevent receipt or accumulation of debris in the tubular barrel portion following installation, such as the wheel hub assembly described below. In such applications, the barrel portion may be sealed by partially filling the barrel portion with a suitable polymer and the preferred method of this invention then includes deforming the free end portion of the tubular barrel portion radially inwardly and toward the body portion of the fastener element to overlie and preferably contact the polymer, preventing receipt of debris in the barrel portion. Where the fastener element is a male fastener element having a solid body portion defining a bottom wall of the tubular barrel portion, the polymer is preferably cast in the tubular barrel portion.
The fastener element and panel assembly formed by the method of this invention thus includes a panel having an opening therethrough, a fastener element having a body portion disposed in the panel opening and an integral tubular barrel portion extending from the panel opening having an intermediate portion integral with the barrel portion and a free end portion. The midportion of the tubular barrel portion is bowed outwardly having a major diameter greater than the inside diameter of the panel opening and the free end portion extends radially inwardly from the midportion forming an inwardly opening annular arcuate hook-shape preventing withdrawal of the fastener element from the panel opening. In the most preferred embodiment of the fastener element and panel assembly, the body portion has an outer diameter greater than the inner diameter of the opening through the panel forming a secure interference fit or mechanical interlock between the body portion and the panel providing excellent torque resistance and preventing push-through of the fastener through the panel opening.
As described above, the fastener element may be a male fastener element having a shank portion integral with and extending from the body portion opposite the tubular barrel portion. The hook-shaped tubular barrel portion may be substantially completely filled with a suitable polymer preventing entry of debris and the free end portion of the tubular barrel portion may then overlie and contact the polymer.
The fastener element and panel assembly and method of forming a fastener element and panel assembly of this invention thus provides several advantages over the prior art, particularly in applications requiring rigid attachment of a fastener element to a thick metal panel or plate and wherein the method of assembly does not deform or mar the panel, such as the wheel hub assembly described hereinbelow. Other advantages and meritorious features of the present invention will be more fully understood from the following description of the preferred embodiments, the appended claims and the drawings, a brief description of which follows.